Re: [PATCH for-9.0] docs/about: Mark the iaspc machine type as deprecated
Am 28. März 2024 14:09:52 UTC schrieb Mark Cave-Ayland
<mark.cave-ayland(a)ilande.co.uk>:
On 27/03/2024 07:09, Gerd Hoffmann wrote:
> On Tue, Mar 26, 2024 at 01:30:48PM +0000, Mark Cave-Ayland wrote:
>> Heh I've actually been using isapc over the past couple of weeks to fire up
>> some old programs in a Windows 3 VM :)
>
> I'm wondering why these use cases can't simply use the 'pc' machine
> type?
>
> The early pci chipsets of the 90-ies have been designed in a
> backward-compatible manner, with devices such as the IDE controller
> being mapped to the standard ISA ioports. So even an historic OS which
> does not know what PCI is can run on that hardware, by simply talking to
> devices using the standard ISA io ports ...
Hmmm that's a fair point: I think the pc machine has a PCI-ISA bridge included, so ISA
devices can be plugged in as needed. The reason I ended up on that configuration was
because I ended up chasing down a regression, and wanted to quickly eliminate things such
as ACPI.
In theory you could pass `-M acpi=off` to not instantiate the PIIX4 ACPI function,
essentially turning the Frankenstein-PIIX4 SB into a PIIX3. However, this also removes SMI
registers used by SeaBIOS to handle SMM setup which may create unwanted side effects. On a
real PIIX3, these registers are located in the ISA function. I wonder if it made sense to
implement that for greater compatibility.
What do you think? Gerd, what do you think w.r.t. SeaBIOS?
Best regards,
Bernhard
>
>
>ATB,
>
>Mark.
>
>